The class of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon is known in the art. Such polymers were produced by Nozaki in the presence of arylphosphine complexes of palladium moieties and certain inert solvents. U.S. Pat. No. 3,694,412 is illustrative. More recently, these linear alternating polymers have become of greater interest because of the greater availability of the polymers. The more recent processes for the production of the linear alternating polymers, now becoming known as polyketones or polyketone polymers, are illustrated by a number of published European Patent Application Nos. including 121,965, 181,014, 213,671 and 257,663. The process, now broadly conventional, comprises the use of a catalyst composition formed from a compound of a Group VIII metal selected from palladium, cobalt or nickel, the anion of a non-hydrohalogenic acid having a pKa below about 6, preferably below 2, and a bidentate ligand of phosphorus, arsenic or antimony. The scope of the polymerization process is extensive but, without wishing to be limited, a generally preferred catalyst composition is formed from a compound of palladium, particularly a palladium alkanoate such as palladium acetate, the anion of trifluoroacetic acid or p-toluenesulfonic acid and a bidentate ligand of phosphorus selected from 1,3-bis(diphenylphosphino)propane or 1,3-bis[di(2-methoxyphenyl)phosphino]-propane.
The resulting polyketone polymers are relatively high molecular weight material having established utility as premium thermoplastics in the production of a variety of shaped articles, e.g., containers as for food and drink, by methods well known for the processing of thermoplastics such as extrusion, injection molding or thermoforming.
In a typical polymerization process the monomer reactants are contacted in the presence of the catalyst composition in an inert reaction diluent such as methanol. The methanol as containers the reaction diluent but also as a primary solvent for the catalyst composition. For the latter purpose, a second solvent such as an aromatic hydrocarbon, e.g., toluene, is optionally present. U.S. Pat. No. 4,921,938, , exemplifies the use of a polar aprotic solvent in the production of catalyst composition solutions. The activity of the catalyst composition and/or the stability of the catalyst composition depends upon a number of factors including the particular catalyst composition components employed, the order in which the components are mixed and the particular reaction diluent employed. In the case of bidentate phosphorus ligands which are hydrocarbyl, e.g., 1,3-bis(diphenylphosphino)propane, in a lower alkanol reaction diluent, catalyst compositions in which the phosphine, then the palladium salt and finally the acid containing the desired anion are provided demonstrate higher activity than catalyst compositions prepared by a different order of mixing. Consecutive samples of such a catalyst solution in alkanol when produced in bulk will show a decrease in activity as well as produce products of decreasing limiting viscosity number (LVN) which is a measure of molecular weight. This apparent lack of storage stability is detrimental when it is desired to conduct a number of polymerizations from a single catalyst composition preparation. It would be of advantage to provide catalyst compositions of relatively constant high activity and which exhibit greater stability over time.